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1.
Nearest neighbor (NN) methods are widely employed for drawing inferences about spatial point patterns of two or more classes. We introduce a method for testing reflexivity in the NN structure (i.e., NN reflexivity) based on a contingency table which will be called reflexivity contingency table (RCT) henceforth. The RCT is based on the NN relationships among the data points and was used for testing niche specificity in literature, but we demonstrate that it is actually more appropriate for testing the NN reflexivity pattern. We derive the asymptotic distribution of the entries of the RCT under random labeling and introduce tests of reflexivity based on these entries. We also consider Pielou’s approach on RCT and show that it is not appropriate for completely mapped spatial data. We determine the appropriate null hypotheses and the underlying conditions/assumptions required for all tests considered. We investigate the finite sample performance of the tests in terms of empirical size and power by extensive Monte Carlo simulations and illustrate the methods on two real-life ecological data sets. 相似文献
2.
The testing for an association between two categorical variables using count data is commonplace in the behavioral sciences.
Here, we present evidence that influential biostatistical textbooks give contradictory and incomplete advice on good practice
in the analysis of such contingency table data. We survey the statistical literature and offer guidance on such analyses.
Specifically, we call for greater use of exact testing rather than tests which use an asymptotic chi-squared distribution.
That is, we suggest that researchers take a conservative approach and only perform asymptotic testing where there is little
doubt that it is appropriate. We recommend a specific criterion for such decision-making. Where asymptotic testing is appropriate,
we recommend chi-squared over the G-test and recommend against the implementation of Yates (or any other) correction. We also
provide advice on the effective use of exact testing for associations in contingency tables. Lastly, we highlight issues that
need to be considered when using the commonly recommended Fisher’s exact test. 相似文献
3.
We develop a spectral framework for testing the hypothesis of complete spatial randomness (CSR) for a spatial point pattern. Five formal tests based on the periodogram (sample spectrum) proposed in Mugglestone (1990) are considered. A simulation study is used to evaluate and compare the power of the tests against clustered, regular and inhomogeneous alternatives to CSR. A subset of the tests is shown to be uniformly more powerful than the others against the alternatives considered. The spectral tests are also compared with three widely used space-domain tests that are based on the mean nearest-neighbor distance, the reduced second-order moment function (K-function), and a bivariate Cramér-von Mises statistic. The test based on the scaled cumulative R-spectrum is more powerful than the space-domain tests for detecting clustered alternatives to CSR, especially when the number of events is small. 相似文献
4.
Robin C. Puett Andrew B. Lawson Allan B. Clark James R. Hebert Martin Kulldorff 《Environmental and Ecological Statistics》2010,17(3):303-316
Many statistical tests have been developed to assess the significance of clusters of disease located around known sources
of environmental contaminants, also known as focused disease clusters. The majority of focused-cluster tests were designed
to detect a particular spatial pattern of clustering, one in which the disease cluster centers around the pollution source
and declines in a radial fashion with distance. However, other spatial patterns of environmentally related disease clusters
are likely given that the spatial dispersion patterns of environmental contaminants, and thus human exposure, depend on a
number of factors (i.e., meteorology and topography). For this study, data were simulated with five different spatial patterns
of disease clusters, reflecting potential pollutant dispersion scenarios: (1) a radial effect decreasing with increasing distance,
(2) a radial effect with a defined peak and decreasing with distance, (3) a simple angular effect, (4) an angular effect decreasing
with increasing distance and (5) an angular effect with a defined peak and decreasing with distance. The power to detect each
type of spatially distributed disease cluster was evaluated using Stone’s Maximum Likelihood Ratio Test, Tango’s Focused Test,
Bithell’s Linear Risk Score Test, and variations of the Lawson–Waller Score Test. Study findings underscore the importance
of considering environmental contaminant dispersion patterns, particularly directional effects, with respect to focused-cluster
test selection in cluster investigations. The effect of extra variation in risk also is considered, although its effect is
not substantial in terms of the power of tests. 相似文献
5.
Often in colonial seabirds, all colony members are believed to defend against nest predators and experience equal nest predation
risk. However, the variation of defense behavior among members and its reproductive consequences are largely unknown. We investigated
(1) individual variation in the nest defense of breeding Black-tailed Gulls Larus crassirostris against a natural egg predator, the Jungle Crow Corvus macrorhynchos and (2) how this behavioral variation affects an individual’s own nest predation risk and that of their neighbors. Results
were compared between 2 years where crow attack levels were manipulated to average 5 and 22 times normal rates (“low” and
“high” predation risk years, respectively) by the placement of varying numbers of artificial nests containing unguarded eggs
at the perimeter of the gull colony. In both years, 23–38% of parents, mostly males, showed “aggressive” defense behavior
(strikes or chases) against crows and decoys. Other “non-aggressive” gulls showed no defense. In the year of low predation
risk, intrusion rates by crows (landing within 0.5 m of an individual gull’s nest) were similar for aggressive and non-aggressive
gulls. In the year of high predation risk, however, the rates of intrusion for aggressive gulls (4%) and for non-aggressive
gulls with an aggressive neighbor (37%) were significantly lower than for non-aggressive gulls without an aggressive neighbor
(76%). These results indicate that aggressive individuals reduce nest predation risk for themselves and conspecific neighbors
in a colonially breeding species. 相似文献
6.
Roman M. Wittig Catherine Crockford Robert M. Seyfarth Dorothy L. Cheney 《Behavioral ecology and sociobiology》2007,61(6):899-909
Theory predicts that females in species with matrilineal dominance hierarchies should use nepotistic support systems to maintain
their family’s rank. Female Old World monkeys, however, form alliances against other females at surprisingly low rates. Nonetheless,
in many species, females utter threat vocalizations when observing others’ disputes, suggesting that these vocalizations may
function as ‘vocal alliances’. We describe a playback experiment testing the efficacy of vocal alliances in free-ranging female
baboons. Subjects were played the same female’s threat-grunts under three separate conditions: after being threatened by the
signaller’s close relative to mimic kin support, after being threatened by a female maternally unrelated to the signaller
to mimic non-kin support, and after a friendly interaction with the signaller’s close relative as a control. Subjects responded
more strongly to the playback and avoided the signaller and her matrilineal relatives for a longer period of time in kin support
trials than in either non-kin support or no aggression trials. In contrast, there was no difference in subjects’ behaviour
between non-kin support and no aggression trials. These results corroborate observational data showing that vocal support
occurs at a higher rate than physical support in female baboons, and that kin are more likely to provide vocal support than
non-kin. We conclude that vocal support plays a similar role as physical support in the alliances of female baboons. 相似文献
7.
Summary. Anting, the plumage-dipping behavior to which ants (mostly formicines) are commonly subjected by birds (mostly passerines),
is shown in tests with hand-raised Blue Jays (Cyanocitta cristata) and the ant Formica exsectoides to be instinctive: the birds displayed typical renditions of the behavior on the first occasion that they encountered ants.
Evidence is presented supportive of the view that anting is a strategy by which birds render ants fit for ingestion. Formicine
ants are ordinarily protected by their formic acid-containing spray. Being wiped into the bird’s plumage causes them to discharge
that spray, without harm to the bird, to the point of almost total emptying of the glandular sac in which the secretion is
stored. The ants are therefore essentially secretion-free by the time they are swallowed. Further evidence indicates that
it is the ant’s possession of the acid sac that triggers the anting behavior in the bird. If F. exsectoides are surgically deprived of their acid sac, they are eaten by the birds without first being subjected to anting. Data are
also presented indicating that the ant’s crop, which is especially capacious in formicines (its contents may amount to over
30% of the formicine’s mass), and which appears to survive the anting procedure intact, constitutes, at least when laden,
a valuable component of the trophic package that the bird accesses by anting. 相似文献
8.
Mangrove conservation and management is a stupendous task chiefly due to the inaccessibility and the hostile substrate conditions.
Remote sensing technology serves as an important tool in providing fast, accurate and up-to-date baseline information on the
status of mangroves. It is almost impossible to carry out conventional field surveys in these swampy areas. The present study
aims at the classification and mapping of the mangroves in Sunderban Biosphere Reserve (SBR) in the West Bengal province of
India using IRS 1D LISS-III satellite data. Different classification approaches, viz., on-screen visual interpretation, supervised and unsupervised classifications were tried. The study showed that four mangroves
classes, viz., Avicennia, Phoenix, mixed mangroves, and mangrove scrub and eight non-mangrove classes could be delineated using all the three approaches. All
the mangrove and non-mangrove classes were field verified and the overall accuracy as well as user’s and producer’s accuracies
for each category were determined. It was observed that among the three approaches, on-screen visual interpretation yielded
higher classification accuracy (91.67%) compared to supervised (79.90%) and unsupervised classifications (71.08%). The results
obtained through on-screen visual interpretation showed that all mangrove categories together cover 23.21% of the total geographical
area of SBR, of which the mixed mangrove category covers maximum area (18.31%). Among the non-mangrove classes, the waterbody
occupies largest area (35.36%) followed by agriculture (34.51%). 相似文献
9.
Gábor Herczeg Abigél Gonda Jarmo Saarikivi Juha Merilä 《Behavioral ecology and sociobiology》2006,60(3):405-414
According to Huey and Slatkin’s [Q Rev Biol 51:363–384, 1976] cost–benefit model of behavioural thermoregulation, lizards should adjust their thermoregulatory strategy between active thermoregulation and thermoconformity (no thermoregulation) according to the costs (time and energy spent thermoregulating, exposure to predators), benefits (optimised physiological performance) and thermal quality of environment associated with a given situation. However, Gilchrist’s [Am Nat 146:252–270, 1995] model of thermal specialisation suggests that apparently costly mechanisms of behavioural thermoregulation can greatly increase fitness if the optimal body temperature is achieved. Field studies of ectotherm thermoregulatory strategies under extreme cold conditions and experiments testing the effects of cool environments on thermoregulatory behaviour are surprisingly scarce. We conducted laboratory experiments to test if common lizards Zootoca
vivipara (an active thermoregulator in the field) are able to switch between active thermoregulation and thermoconformity in response to different thermal environments. We found that lizards in treatments with an opportunity to reach their preferred body temperature thermoregulated accurately, maintained their level of daily activity and improved their body condition considerably. In contrast, lizards in the treatment where the preferred body temperature could not be reached became thermoconformers, decreased their daily activity (except for gravid females) and did not increase their body condition. Our results show that lizards can indeed change their thermoregulatory strategy but stress that maintaining the preferred body temperature and, thus, optimising the physiological performance have high priority in lizard behaviour. 相似文献
10.
Oscar Castro-Orgaz 《Environmental Fluid Mechanics》2011,11(4):427-435
Seepage flow is an agent related to the transport and dispersion of contamination in groundwater. Steady two-dimensional seepage
flow is governed by Laplace’s equation, for which several solution techniques are available. Because computations are complex
from a practical point of view, simplified models encompass the Dupuit-Forchheimer approach assuming a horizontal flow. However
this approach is inaccurate in seepage problems involving steep drawdowns. In this research, a new theoretical model for 2D
seepage flow is proposed based on Fawer’s theory for curved flows Castro-Orgaz (Environ Fluid Mech 10(3):2971–2310, 2010),
from which a second-order equation results describing the seepage surface. From this development, a numerical solution for
the rectangular dam problem based on the second-order model is presented, whereas a simple first-order equation is found to
describe flow to drains under a uniform rainfall. The results of this new model are compared with the full 2D solution of
Laplace’s equation for typical test cases, resulting in an excellent agreement. 相似文献
11.
Fitting generalised linear models (GLMs) with more than one predictor has become the standard method of analysis in evolutionary
and behavioural research. Often, GLMs are used for exploratory data analysis, where one starts with a complex full model including
interaction terms and then simplifies by removing non-significant terms. While this approach can be useful, it is problematic
if significant effects are interpreted as if they arose from a single a priori hypothesis test. This is because model selection
involves cryptic multiple hypothesis testing, a fact that has only rarely been acknowledged or quantified. We show that the
probability of finding at least one ‘significant’ effect is high, even if all null hypotheses are true (e.g. 40% when starting
with four predictors and their two-way interactions). This probability is close to theoretical expectations when the sample
size (N) is large relative to the number of predictors including interactions (k). In contrast, type I error rates strongly exceed even those expectations when model simplification is applied to models
that are over-fitted before simplification (low N/k ratio). The increase in false-positive results arises primarily from an overestimation of effect sizes among significant
predictors, leading to upward-biased effect sizes that often cannot be reproduced in follow-up studies (‘the winner's curse’).
Despite having their own problems, full model tests and P value adjustments can be used as a guide to how frequently type I errors arise by sampling variation alone. We favour the
presentation of full models, since they best reflect the range of predictors investigated and ensure a balanced representation
also of non-significant results. 相似文献
12.
Skeletochronological analysis of Kemp’s ridley (Lepidochelys kempii) and loggerhead (Caretta caretta) sea turtle humeri and scleral ossicles was conducted to (1) describe the characteristics of scleral ossicles in these species,
(2) determine whether the scleral ossicles contain annually deposited skeletal growth marks and (3) evaluate the potential
for skeletochronological analysis of ossicles to obtain age data for size classes and species of sea turtles whose humeri
exhibit prohibitive amounts of growth mark resorption. Humeri, entire eyes, and/or individual scleral ossicles were collected
from stranded, dead sea turtles that were found along the coasts of Florida, North Carolina, Virginia, and Texas, USA. Samples
were taken from a total of 77 neritic, juvenile Kemp’s ridleys ranging from 21.1 to 56.8 cm straightline carapace length (SCL),
as well as two Kemp’s ridley hatchlings. For loggerheads, samples were obtained from 65 neritic juvenile and adult turtles
ranging from 44.7 to 103.6 cm SCL and ten hatchlings. Examination of the ossicles revealed the presence of marks similar in
appearance to those found in humeri. The number of marks in the ossicles and humeri of individual juvenile Kemp’s ridleys
for which both structures were collected (n = 55) was equivalent, strongly indicating that the marks are annual. However, in large juvenile and adult loggerhead turtles
(n = 65), some significant resorption of early growth marks was observed, suggesting that although ossicles might be useful
for skeletochronological analysis of small juveniles, they may not provide a reasonable alternative to humeri for obtaining
age estimates for older loggerhead sea turtles. 相似文献
13.
The purpose of this paper is to develop a set of associated statistical tests for spatial clustering. In particular, a set
of three associated tests will be developed; these will correspond to the three types of tests set out by Besag and Newell
(general tests, focused tests, and tests for the detection of clustering). The associated tests draw primarily, though not
exclusively, upon existing tests and results. The principal contributions are based upon the score statistic for focused tests,
which has been an important approach to testing for clustering around environmental hazards. The first contribution consists
of the formulation of a global statistic for general tests that corresponds to focused score statistics, along with an assessment
of the distribution of the statistic under the null hypothesis of no raised incidence. The local score statistics used for
focused tests will have the property of summing to the global statistic used for the corresponding general test. Attention
is also given to the maximum local score statistic for the “test for the detection of clustering”. The critical values of
this statistic which are required for testing the null hypothesis are described. Application of the methods is made to leukemia
data for central New York State. 相似文献
14.
Animals’ contest performance is influenced by their recent contest experiences. This influence could either be exerted by
individuals re-estimating their own fighting ability (self-assessment) or by their opponents responding to status-related
cues (social-cue mechanism) or both. Individuals of Kryptolebias marmoratus, a hermaphroditic killifish, were given different contest experiences to examine how two opponents’ prior experiences combined
to determine their contest interaction and to test both of these mechanisms as potential causes of the observed experience
effect. Our data showed that losers’ decisions to retreat at different stages of a contest were influenced by their own but
not by the winners’ contest experience—a result consistent with self-assessment but not with the social-cue mechanism. An
association between the fish initiating and winning contests thus probably arose because both were correlated with an individual’s
assessment of its fighting ability, but not because initiating contests made opponents more inclined to retreat. 相似文献
15.
Behavioral ecologists are often faced with a situation where they need to compare the central tendencies of two samples. The
standard tools of the t test and Mann–Whitney U test (equivalent to the Wilcoxon rank-sum test) are unreliable when the variances of the groups are different. The problem
is particularly severe when sample sizes are different between groups. The unequal-variance t test (Welch test) may not be suitable for nonnormal data. Here, we propose the use of Brunner and Munzel’s generalized Wilcoxon
test followed by randomization to allow for small sample sizes. This tests whether the probability of an individual from one
population being bigger than an individual from the other deviates from random expectation. This probability may sometimes
be a more clear and informative measure of difference between the groups than a difference in more commonly used measures
of central tendency (such as the mean). We provide a recipe for carrying out a statistical test of the null hypothesis that
this probability is 50% and demonstrate the effectiveness of this technique for sample sizes typical in behavioral ecology.
Although the test is not available in any commercial software package, it is relatively straightforward to implement for anyone
with some programming ability. Furthermore, implementations in R and SAS are freely available on the internet. 相似文献
16.
A recently favored hypothesis is that duetting in birds has a mate-guarding function: a male responds vocally to his partner’s
song, thereby forming a duet that repels males who are attracted to her song. Previous studies have not provided unambiguous
tests of the mate-guarding hypothesis because: (1) the probability of a male answering his partner’s song has not been shown
to increase specifically when the female is fertile, and (2) the probability of a male answering his partner’s song has not
been assessed separately from simply a higher song initiation rate. We investigated extra-pair paternity, mate-guarding, and
duetting in the socially monogamous Australian magpie-lark (Grallina cyanoleuca). DNA fingerprinting revealed that 3% of young were the result of extra-pair paternity, and we found that males guarded fertile
females by staying close to them. However, males did not initiate songs at a higher rate when females were fertile and actually
reduced their probability of replying to female song during this period. We conclude that although male magpie-larks did guard
fertile females in an attempt to prevent extra-pair copulations, they did not use duetting for this purpose.
Received: 10 May 1999 / Received in revised form: 27 September 1999 / Accepted: 2 October 1999 相似文献
17.
Ecological data often involve measurements taken at irregularly spaced locations (e.g., the heights of trees in a forest).
A useful approach for modeling such data is via a marked point process, where the marks (i.e., measurements) and points (i.e.,
locations) are often assumed to be independent. Although this is a convenient assumption, it may not hold in practice. Schlather
et al. (Journal of the Royal Statistical Society Services B, 66, 79–93, 2004) proposed a simulation-based approach to test
this assumption. This paper presents a new method for testing the assumption of independence between the marks and the points.
Instead of considering a simulation approach, we derive analytical results that allow the test to be implemented via a conventional
χ2 statistic. We illustrate the use of our approach by applying it to an example involving desert plant data. 相似文献
18.
Sperm competition is predicted to generate opposing selection pressures on males. On one hand, selection should favour ‘defensive’ adaptations that protect a male’s ejaculate from displacement, while, on the other hand, selection should favour ‘offensive’ adaptations that overcome paternity assurance mechanisms of rivals. Here, we use the sterile male technique to assess sperm precedence when a male dung beetle Onthophagus taurus mates in both a defensive (first male) and an offensive (second male) role. Significant variation in a male’s sperm precedence (both P
1 and P
2) was detected, and an individual’s defensive (P
1) and offensive (P
2) abilities were positively correlated. Thus, it appears that sexual selection simultaneously selects for ‘defensive’ and ‘offensive’ adaptations in O. taurus. We discuss a variety of male traits in O. taurus that potentially contribute to a male’s ability to be successful when mating in an ‘offensive’ and a ‘defensive’ role. 相似文献
19.
Katrin Strauss Holger Scharpenberg Robin M. Crewe Felix Glahn Heidi Foth Robin F. A. Moritz 《Behavioral ecology and sociobiology》2008,62(9):1523-1531
Queen pheromones interfere with worker reproduction in social insects. However, there is still an unresolved question as to
whether this pheromone acts as an “honest” signal for workers, giving a reliable indication of the queen’s reproductive value,
or as a suppressive agent, inhibiting worker reproduction independent of the queen’s reproductive capacity. In honeybees (Apis mellifera), the queen’s mandibular gland secretion, a mix of fatty acids and some aromatic compounds, is crucial for regulating the
reproductive division of labor in the colony inhibiting ovary development in workers. We quantified the mandibular gland secretions
of virgin, drone-laying, and naturally mated queens using gas chromatography to test whether the queens’ mating, ovary activation,
or the reproductive value for workers correlated with the composition of the secretion. Although the absolute amounts of the
“queen substance” 9-oxo-2(E)-decenoic acid (9-ODA) were similar among the three groups, the proportions of 9-ODA decreased
with increasing reproductive quality. Furthermore, the ratios of queen to worker compounds were similar in all three treatment
groups, irrespective of the reproductive capacity. A multivariate analysis including all six compounds could not separate
drone-laying queens from naturally mated ones, both with active ovaries but only the latter ensuring colony survival. We suggest
that the mandibular gland pheromones are unlikely to function as reliable indicators of queen reproductive value and rather
operate as an agent to suppress worker reproduction. This does not exclude the possibility that other “honest” pheromone signals
exist in the honeybee colony, but these would have to arise from other semiochemicals, which could be produced by both the
queen and the brood. 相似文献
20.
The effects of testosterone on antibody production and plumage coloration in male house sparrows (Passer domesticus) 总被引:9,自引:3,他引:6
Many bird species have patches of colour in their plumage, contrasting with their basic coloration, which are used to display
and signal status to conspecifics. These are called ’badges of status’, because they are believed to be low-cost signals of
social status. For a signalling system to be evolutionarily stable, cheating must be controlled. The conventional view is
that there is frequent testing, which uncovers cheats. Recently, the immunocompetence handicap hypothesis (ICHH) suggested
that signals may be dependent on testosterone for their development, with a cost being imposed through immune suppression.
We report experiments on house sparrows (Passer domesticus) which show that testosterone significantly influences the size of the bib (a ’badge of status’). The ultimate effect of
the testosterone manipulation was to impair antibody production, as predicted by the ICHH. However, testosterone manipulations
also changed the levels of the ’stress hormone’ corticosterone. The level of corticosterone was also related to the degree
of immunosuppression. After controlling for the effect of corticosterone, testosterone enhanced the birds’ ability to produce
antibodies, counter to the ICHH. The hypothesis therefore must be modified. We suggest that testosterone has a dual effect:
it leads to immunosuppression through a mechanism involving corticosterone but, conversely, leads to increased immunocompetence
probably via dominance influencing access to resources.
Received: 5 March 1999 / Received in revised form: 1 October 1999 / Accepted: 16 October 1999 相似文献